Update the charms used in the test
Update the charms used in the test

to have a consistent behavior. Wordpress is not stable enough anymore
to consistently deploy without a problem. And when there's a problem,
then the deploy & add-relation often work, but remove-saas almost
always fails when the unit's agent is in 'idle' but the workload is in
'error'.

juju/python-libjuju,juju/python-libjuju